1. Field of the Invention
The invention relates to a method of producing a contact terminal provided with at least a first contact surface for contacting with a mating contact area, comprising at least the step of stamping the contact terminal from a flat blank metal having a substantially flat surface with a predetermined first width, the first contact surface being substantially perpendicular to the flat surface.
2. Brief Description of Prior Developments
Such a method is known in the connector manufacture industry. In this industry, it is fully acknowledged that the opposing contact members need to have low surface roughness for reduced wear to ensure a low (stable) contact resistance even after many operational mating cycles. To achieve the desired connector performance, not only are the topography and coating thickness of the plating on contact surfaces of importance, but also the surface roughness of the underlying substrate contact material. It is well known that the intrinsic surface roughness of a copper alloy strip, as received from the material vendor after milling operation, has along the plane of rolling a low roughness value of the order of one-tenth of a micrometer. In-coming material inspection for this parameter, among others such as dimension and tensile strength etc., is a primary means to predict future performance and usability, for sophisticated connector applications.
Once this material is fed to a die for stamping operation to produce a contact terminal of pre-determined shape, its roughness increases in areas where it has been in contact with die tooling. The resulting roughness depends on the surface roughness of the tool used and any associated die operation (i.e. bend, coin, slug punch-out etc.). In these typical die operations, for example material drag through opposing die-platen results in the least increase in roughness. Contrary to this, for areas which have been subjected to a punch or cut-out operation, a substantial roughness increase (burr) formation is expected. This is attributed to shear-fracture crack-propagation related to a complex function of material thickness, material properties, stamping speed and the dimensional difference (clearance) between the punch and die recess. As is known to persons skilled in the art, any resultant stamped edge is imperfect. Under normal circumstances, this fractured edge, due to its high roughness, without further precautions is unsuitable as a contacting surface of the connector members as applicable in electrical connector manufacture.
The resulting roughness and burrs or undulating peaks on such contact surfaces can be somewhat smoothened by coating the terminal with a predetermined suitable metal (e.g. gold). However, in the case of opposing contact beams of a dual beam tuning-fork type terminal, the gap size cannot be made smaller than about 0.8 mm. Such gaps are required to ensure adequate electrolytic fluid movement, hence allowing metal deposition on the contacting surfaces. In such a process, one could electrolytically deburr or etch the beams locally in the gap area. However, as a final part of this process one needs to decrease the gap for example by bending the terminal beams more angularly towards each other. However, with such a process the contact surface width is equal to the original material thickness, i.e., about 0.2 mm. Since a male type terminal is often a pin with a rectangular cross section with a width of about 0.4 mm, such 0.2 mm wide contact surfaces of the tuning-fork type terminal (with a width at contact surface substantially similar to that of the pin) would act like a "knife" on the plated coating of the mating male terminal. For a typical male type terminal having a circular cross section such tuning-fork type terminals are not suitable at all since they would slip away from the surface of the mating male terminal unless such pins are constrained, for example, by the housing cavity.
To avoid problems of contact surface roughness and relatively smaller contact surface width, conventionally connector designers prefer to locate the contact surface of contact terminals along the flat-rolled plane of the material. One example of such a prior art contact terminal is a box-type contact terminal 41, as is schematically shown in FIG. 1b. The stamping is in such a way as to have a U-shaped cross section. Such a box-type terminal 41 is provided with a dual-beam receptacle contact with two opposing cantilever spring beams 42, 43 having a specific gap (under-size) to cooperate with a mating (over-size) male pin (not shown in FIG. 1b), to result in a specified contact normal force. If the cross-section of the mating pin is round in the contact area, the opposing receptacle contact zone is flat. Should the pin be substantially flat over the contact zone, the corresponding contact area of the receptacle needs to be curved--which in practice usually is a spherical dimple (not shown) on the flat-rolled portion of stamped strip cantilever beams 42, 43 of this dual-beam contact.
Besides positioning receptacle (female-type) and pin (male-type) contacts in plastic housings of a connector, cavity entry lead-in geometry openings for the connector are important to mutually guide opposing mating connector parts during insertion/withdrawal cycling. Additional provision on the terminals to facilitate appropriate contact mating is to have a lead-in entry throat for the receptacle contact, to cooperate with the taper at the extremity of the pin.